1. Field of the Invention
The present invention relates to a tub having a structurally strengthened rear wall and a washing machine with the same therein, and more particularly, to a tub injection-molded with a bearing housing inserted supporting a shaft to rotate a drum.
2. Discussion of the Related Art
In general, a drum type washing washes laundry by using a friction force between a drum rotated by a driving power of a motor and the laundry in a state detergent, washing water, and the laundry are introduced into the drum, shows almost no damage to, and entangling of the laundry, and has pounding, and rubbing washing effects.
In the related art drum type washing machines, there are an indirect drive type in which the driving power of the motor is transmitted to the drum through a belt wound on a motor pulley and a drum pulley indirectly, and a direct drive type in which the brushless DC (BLDC) motor is connected to the drum directly, to transmit the driving power of the motor to the drum, directly.
The type in which the driving power of the motor is transmitted to the drum, not directly, but indirectly through the motor pulley and the drum pulley, has much energy loss in the course of power transmission, and causes much noise in the course of power transmission.
According to this, it is the present trend that use of the direct drive type drum type washing machines with the BLDC motor is increasing, for solving the problems of the indirect drive type drum type washing machines. A related art direct drive type drum type washing machine will be described with reference to FIG. 1, briefly. FIG. 1 illustrates a longitudinal section of a related art drum type washing machine.
Referring to FIG. 1, the related art drum type washing machine is provided with a tub 2 mounted inside of a cabinet 1, and a drum 3 rotatably mounted on a central part of an inside of the tub 2. There is a motor in rear of the tub 2, wherein a stator 6 is fixed to a rear wall of the tub, and a rotor 5 surrounds the stator 6, and is connected to the drum 3 with a shaft passed through the tub.
Together with these, there is a metallic tub supporter between a tub rear wall and the stator having a shape almost the same with an outer shape of the tub rear wall fixed to the tub rear wall in fastening the stator for supporting a load of the stator, and maintaining a concentricity of the stator.
In the meantime, there are a door 21 mounted on a front part of the cabinet 1, and a gasket 22 between the door 21 and the tub 2.
There are a hanging spring 23 between an inside surface of an upper part of the cabinet 1, and an upper part of an outside circumferential surface of the tub 2, and a friction damper 24 between the inside surface of a lower part of the cabinet 1, and a lower part of the outside circumferential surface of the tub 2.
FIG. 2 illustrates a perspective outside view of the stator in FIG. 1, and FIG. 3 illustrates a perspective view of a sectional type core SC applied to the stator in FIG. 2.
In a related art method for fabricating the stator core, a sheet of metal plate is pressed to form a unit core having tooth portions 151, a base part 150, and a round part 500 opposite to the tooth portions 151 for forming fastening hole 500a therein, the unit cores are stacked to form a unit core assembly, and the unit core assemblies are connected to each other in a circumferential direction, to complete fabrication of the stator core, called the sectional type core SC.
The round part provides the fastening hole 500a for fixing the stator 6 to the rear wall of the tub, and enduring a fastening force of a bolt.
However, the method for fabricating the stator 6 by means of the sectional type cores SC has, not only a complicate fabrication process, but also loss of much material.
Therefore, even if a helical type core HC is favorable, in which a sheet of steel plate having the tooth portions 151 and the base part 150 is stacked turning in a helix, since it is required to bend the sheet of metal punched out in a form of a band into the helix, the helical type core has a drawback in that the round part for fixing the stator to the tub can not be formed on an inner side of the core.
This is because, if the round part 500 is formed on the inner side of the core in fabrication of the helical core HC, a large width of the core at a part having the round part formed thereon impedes bending of the core.
Therefore, currently, a stator structure is required, in which a function the same with the round part of the sectional type core SC is made to be carried out, not by the core itself, but by other part, for employing the helical type core HC.
For reference, a reason why it is important to secure an adequate rigidity of the round part having the fastening hole formed in for fixing the stator to the tub is as follows.
The washing machine that rotates the drum directly by using the BLDC motor has the stator mounted on a rear part of the tub, directly. In a case of the motor for a large capacity drum type washing machine with more than 1.5 kg of stator net weight, and a spinning speed in a range of 600-2000 RPM, it is liable that a bolt fastened part of the stator 6 is broken due to the stator weight, vibration in the high speed rotation, and shaking and deformation of the rotor 5.
Particularly, in a case of the drum type washing machine, in which the BLDC motor is used, and the stator 6 is fixed to the tub rear wall, where an axis direction of the stator 6 is substantially parallel to ground, the vibration generated in operation of the washing machine causes intensive damage to the fastening part of the stator 6 to the tub rear wall.
Thus, an adequate rigidity of the round part having the fastening hole formed therein is very important in fixing the stator 6 to the tub.
In the meantime, in a trend a capacity of the drum type washing machine becomes larger as the time goes by, there have been many problems, such as even the tub to which the stator is fastened is damaged in a case the stator has a weight more than 1.5 kg in a structure the axis of the stator is parallel to the ground like the drum type washing machine.
Therefore, in order to prevent occurrence of the damage, in the related art structure, in general a metal tub supporter is lined, when a process for fastening the tub supporter to the tub rear wall is required in addition to an assembly line, that drops a productivity.
FIG. 4 illustrates a conventional tub 302, more specifically, an outer surface of the rear wall where the motor is mounted.
As shown in FIG. 4, a circumferential rib 311 and 312 is formed in a circumferential direction on the outer surface of the rear wall of the tub 302, and a radial rib 321 is also formed on the outer surface of the rear wall in a radial direction. The farther the radial rib 321 is from the center of the rear wall, the lower the height thereof is. Thus, the rear wall of the tub may have a problem in its strength and rigidity. Furthermore, the distance between the radial ribs is gradually getting wider from the center thereof. Thereby, the strength of the rear wall of the tub is not high enough and it causes a structural-strength-related problem in the farthest portion of the rear wall from the center.
Also, the thickness between the circumferential rib 311 formed nearer to the center of the rear wall and the circumferential rib 312 formed farther from the center is the same. Since the nearer portion to the center is more affected by the vibration of the shaft than the farther portion, the nearer portion is needed to have much strength and rigidity. Nevertheless, the conventional washing machine fails to solve the above problem.
Moreover, according to the conventional washing machine, the circumferential rib 311 and 312 and the radial rib 321 are formed relatively high to enhance the strength of the rear wall of the tub. However, the higher the ribs are, the more flexible the ribs are. Thereby, the strength or rigidity is not gained as high as structurally required and it causes a structural-strength-related problem as well as high production cost.
Meanwhile, since the inner surface (not shown) of the rear wall of the tub is formed as a smooth surface without ribs, the reinforcement for the strength is dependent on the ribs on the outer surface only. That is one of the reasons why the ribs on the outer surface are high in the conventional washing machine.
The capacity of the tub for holding wash water therein influences the capacity of the washing machine. Here, the capacity of the tub is influenced by the position of the inner surface of the rear wall. Since the conventional rear wall of the tub described above has the inner surface thereof sided toward the drum, the conventional rear wall of the tub has a disadvantage that the tub has a small capacity.
Also, the overall thickness of the rear wall of the tub with the height of the rib considered may affect the disposition of the other components within the limited space of the cabinet.